Does this mean you're keeping Call ducks in an outdoor pen that's not secured on every side and the top? That's very concerning to me if I'm understanding this correctly. Most common owls in the US are easily able to take a Call duck since owls can lift several times their own weight, unlike most raptors. If you have Calls in a pen with sides but no top, they're basically, umm, sitting ducks when it comes to nocturnal predators.
not to mention something just climbing up the sides, scary